Kinetics of Drug Penetration across the Cornea at a Microscopic Level Drugs applied topically to the eye access the intraocular tissues predominantly by penetration across the multi-layered cornea, consisting of a stratified epithelial layer, a thick collagenous stroma and a leaky monolayer of endothelium. Previous studies on topical drug kinetics to the eye have focused mainly on compartmental modeling of transport across the cornea. Such models have disregarded the inherent heterogeneity in the cornea, rendering them incapable of making sufficiently accurate predictions. The disregard for the heterogeneity in the cornea stems from the fact that experimental transcorneal concentration profiles of drugs are unavailable and difficult to obtain. Accordingly, only the average values of the drugs in the cornea, which are usually measured, have been employed in the development of pharmacokinetic modeling of topical drugs to the eye. This project will employ a novel custom-built confocal scanning microfluorometer to measure transcorneal profiles of a series of fluorescent compounds employed as drug analogs across rabbit cornea mounted in vitro. The resulting transcorneal concentration profiles will be employed to develop a phenomenologically-based non-compartmental pharmacokinetic model. The resulting model will then be employed to predict pharmacokinetics for topical administration of the fluorescent drug analogs. These predictions will be compared with in vivo data, which will be obtained for the same fluorescent compounds using another custom-built ocular spot-fluorometer. The latter instrument can measure average fluorescence from the cornea and anterior chamber. Overall, the results from this project involving in vivo and in vitro experiments is expected to yield detailed mechanistic understanding of topical drug kinetics and eventually enable rational drug design as well as the development of optimal drug dosage regimen. PUBLIC HEALTH RELEVANCE: More than 90% of the drugs to the eye are administered by topical administration. In this project, we propose to investigate how the topically administered drugs penetrate across the cornea into the eye. We expect to obtain a mechanistic understanding of the penetration, which is needed for rational drug design and optimal design of dosage regimen.